1. Field of the Invention
The present invention relates to a method of and an apparatus for executing processing such as bonding on a lead frame.
2. Description of the Background Art
FIG. 1 is a perspective view of a conventional lead frame processing apparatus. An apparatus 100 is constructed as a bonding apparatus for feeding in a direction X a lead frame 4 which fixedly carries semiconductor chips SC and for subsequently wire bonding the semiconductor chips SC to the lead frame 4 at a position where a heat block 33 is located.
On the both sides of the heat block 33, two movable guide rails 28 are provided in a faced relation to each other for free movement upward above and downward below a top surface 33a of the heat block 33. In the facing surface of each movable guide rail 28, a guide trench 28a is formed. The guide trenches 28a each have a tapering portion 28b at an end so as to smoothly receive the lead frame 4.
A frame presser member 27 is disposed above the heat block 33. Comprising an up-down mechanism, the frame presser member 27 is movable upward and downward, and hence, is capable of pressing the lead frame 4 against the top surface 33a of the heat block 33.
The two movable guide rails 28 are each faced with at each end a stationary guide rail 29. A guide step 29a is formed in the facing surface of each stationary guide rail 29.
A screw shaft 32b is disposed parallel to the guide rails 28 and 29. Although not shown in FIG. 1, the screw shaft 32b is engageably received by an external screw which is fixed to a holder 32a. Entrance clamp fingers 30a and 30b and exit clamp fingers 31a and 31b are held in the holder 32a at their base portions. The entrance and the exit clamp fingers 30a, 30b, 31a and 31b grip the lead frame 4 therebetween and feed the lead frame 4 on the guide rails 28 and 29. With the external screw driven by a step motor and the like and hence in rotation, the holder 32a reciprocally slides along the guide rails 29, and therefore, the clamp fingers 30a, 30b, 31a and 31b accordingly move back and forth along the guide rails 29 in the feed direction X of the lead frame 4.
&lt;Operation&gt;
FIGS. 2 to 10 are diagrams showing operation of the apparatus 100.
First, the lead frame 4 is forwarded onto the guide trenches 29a of the entrance guide rails 29 by a transportation mechanism not shown (FIG. 2) Next, the lower entrance clamp finger 30a moves upward and the upper entrance clamp finger 30b moves downward so that the entrance clamp is closed (FIG. 3). The screw shaft 32b then rotates to move the upper and the lower entrance clamp fingers 30a and 30b in a direction -X, thereby pushing back and registering the lead frame 4 to a predetermined position (FIG. 4).
The entrance clamp is opened by moving the lower entrance clamp finger 30a downward and the upper entrance clamp finger 30b upward, followed by that the entrance clamp is moved a preselected distance in the direction -X by rotation of the screw shaft 32b (FIG. 5).
The lower and the upper entrance clamp fingers 30a and 30b move toward each other so that the lead frame 4 is fixedly held in a tight nip therebetween (FIG. 6). The screw shaft 32b then reversely rotates, thereby sliding the entrance clamp in the direction +X. Upon feeding of the lead frame 4 by a preselected distance (FIG. 7), the lower and the upper entrance clamp fingers 30a and 30b move away from each other to release the lead frame 4 (FIG. 8).
Thereafter, the entrance clamp again moves in the direction -X by rotation of the screw shaft 32b and return to its position of FIG. 5 (FIG. 9).
By repeated clamping actions of the entrance clamp as shown in FIGS. 2 to 9, the lead frame 4 is intermittently advanced in the direction +X, in the course of which a predetermined portion of the lead frame 4 reaches to a bonding position on the heat block 33 (FIG. 10).
As shown in FIG. 10, the movable guide rails 28 are upwards while waiting for the lead frame 4 to reach at the heat block 33. Hence, the lead frame 4 will see no chance of getting caught in frictional contact with the heat block 33 during transportation therefor onto the heat block 33.
Next, the frame presser member 27 slides down to urge the lead frame 4 against the heat block 33. At the same time, the guide rails 28 also slide downward.
The lead frame 4 as it is held in this manner is wire bonded to the semiconductor chips SC which are mounted on the lead frame 4. Wire bonding is executed through an opening 35 of the frame presser member 27.
The frame presser member 27 moves upward on completion of the wire bonding and the reciprocal motion of the entrance clamp immediately resumes. The lead frame 4 passed the movable guide rails 28 is held between the lower and the upper exit clamp fingers 31a and 31b and fed in the direction +X.
By repeating the process steps above, the semiconductor chips SC mounted on the lead frame 4 are bonded to a corresponding portion of the lead frame 4 one after another.
As heretofore described, in the conventional lead frame processing apparatus 100, several clamping actions of the clamp on the lead frame are needed until the lead frame has been conveyed to the predetermined bonding position. Hence, the lead frame tends to be largely displaced, and as a result, a feeding accuracy of the conventional apparatus becomes poor. In addition, the necessity of the several clamping actions renders the conventional apparatus inefficient in terms of operation time.